1. Field of the Invention
The field of the invention is data processing, or, more specifically, methods, apparatus, and products for tape recording that increases the capacity of an empty area of tape without loss of necessary data.
2. Description of Related Art
In a conventional tape recorder (also called a “tape drive” in the following description), the logical beginning of a tape (BOT), which is the position where data recording starts, is used as the physical beginning of the tape, and data information to be recorded is recorded from this beginning. The information is read when the tape is inserted, and rewinding is performed when the tape is to be ejected. Further, the types of tape recorders include a cartridge type, an open reel type and the like. In addition, some cartridge type tapes (magnetic tapes) include a memory to record system information.
When a magnetic tape drive is used to periodically record backup data or the like, the drive is mainly used to keep only the most recent data while allowing deletion of previously recorded data. In this case, although the proportion of an unnecessary data area becomes large in a front half portion of the tape, the capacity of the front half portion of the tape is unnecessarily consumed in reality due to sequential access.
In this respect, there has been employed a method to manage the capacity of a tape by copying (making a duplicate of) only effective data onto another tape medium (a medium using a tape is broadly termed as a “tape medium”) when the proportion of an unnecessary data area on the tape exceeds a certain amount (such operation is termed as reclaim).
FIG. 10 shows a relationship between an empty area and user data to be written on a tape 1000 by the prior art. Here, the logical beginning of a tape medium, i.e., the write start position, which is the point where data is physically written initially on the tape, is called BOT (Beginning of Tape) 1010. Further, the logical end of the tape, i.e., the write end position, which is the point where data cannot be physically written anymore, is called EOT (End of Tape) 1020. A user data group 1050 on the tape 1000 normally includes a mixture of unnecessary data pieces 1052 and necessary data pieces 1054. The positions of BOT and EOT are always fixed, and the tape drive does not move these positions. This is because the tape drive has no way to determine which data piece is necessary and which data piece is unnecessary among the data pieces written on the tape. Further, the end of actually written data is called EOD (End of Data) 1030. The EOD always exists between the BOT and EOT. The area between the EOD and EOT is a so-called empty area 1040. Normally, the next piece of data is written in this empty area.
Magnetic tape drives often used today, for example, employ a method to write data by moving a write position back and forth many times between the both ends of the single tape while shifting the write position little by little. In this case, the tape has multiple areas each called a partition, and user data can be written in each of the partitions. Note that, such partitions can be created not only in a linear method in which a write position is moved back and forth many times between the both ends of the tape as described above, but also in a helical method in which all data is read or written by single movement of a tape from one end of the tape to the other end thereof as in the case of a video tape.
When each of the positions of the beginning of a partition (BOP) and the end of the partition (EOP) is moved for writing data efficiently on a tape, e.g., when BOP is moved to the back of the tape, there arises a problem that, data existing between the previous position of the BOP and the new position (current position) of the BOP becomes inaccessible.
Japanese Patent Application Publication No. 2002-190163 describes a method for solving a problem of low use efficiency of a tape, which is caused by concentration of access to a certain location in a magnetic tape such as the portion of the beginning thereof. In the method, the position of the logical beginning of a magnetic tape is updated by sequentially moving the position of the logical beginning of the tape. With this method, however, necessary data on the tape may be lost. This is because when the beginning of the tape is updated in this method, there is no operation to move necessary data, and no correspondence is made such as assignment of a record number corresponding to a record being variable-length data.
Japanese Patent Application Publication No. Hei 11-53869 describes a method to avoid reading and writing from and to an unreadable bad data block by providing a tape information management area including management units. The tape information management area is provided in a recordable beginning portion of a magnetic tape (BOT). The management units are configured to register and manage position information on tape marks and position information on unreadable bad data blocks among data blocks. With this method, there remains a problem, however, that the beginning of a tape (BOT) is repeatedly and intensively accessed when the tape is inserted. In addition, this method is considered to be unsuitable for an operation to move the beginning of a tape (BOT).